The present invention relates generally to retraction mechanisms for utility supply lines and more particularly to a dental unit or the like wherein fluid pressure is utilized to retract a utility supply line connected to a dental instrument.
It is well known in dental units to have a dental instrument nested in the unit and connected by a cord, hose etc. to a utility supply. It is desirable in such units to provide a mechanism for retracting or pulling the extended utility supply line back into the dental unit when the dental instrument is being returned to a storage position. Conversely, this mechanism must be relatively friction-free so that when the instrument is being manually pulled from the stored to an in-use position there is little or no resistance to the withdrawal of the utility line from the unit.
Various retraction mechanisms are known which allow for the extension of the utility lines out of the unit when the instrument is being moved to an in-use position and which serves the purpose of automatically retracting the utility supply lines back into the dental unit when the instrument is returned to a storage or out-of-use position.
One type of retraction system utilizes a fluid pressure to provide the retraction force. Such systems are shown for example in U.S. Pat. Nos. 3,722,095, 3,427,719 and 3,391,875. In the '719 and '875 patents, the utility line is operatively connected to a piston within a cylinder. A differential pressure is created across the piston by evacuating the rear end of the cylinder. This pulls the piston into to the cylinder, thereby, drawing the connected utility line into the cylinder for storage. The '095 patent creates a differential pressure across the piston by applying pressure to one end of the cylinder. In this case, however, the piston and cylinder arrangement merely provides a motive force for retracting the utility line and the cylinder does not perform the dual function of acting as the housing for the utility line.
In the present invention, the retraction system operates under positive pressure to move the piston within the cylinder to a stored position. Also, in the present invention, the cylinder itself acts as the storage chamber for the utility line. The withdrawal of the utility line from the cylinder and the accompanied movement of the piston is accomplished relatively friction-free in that a relatively large vent means is provided to permit the free exhaust of air from the cylinder as the piston is pulled toward one end of the cylinder by the utility line. As another feature of the invention, a valve for the vent is constructed so as to provide a relatively large vent area while at the same time occupying a minimum of space so that several cylinders can be placed side by side in a relatively small area.